diff --git a/toonz/sources/include/tcg/poly_ops.h b/toonz/sources/include/tcg/poly_ops.h
index 1825837..741b91a 100644
--- a/toonz/sources/include/tcg/poly_ops.h
+++ b/toonz/sources/include/tcg/poly_ops.h
@@ -5,6 +5,7 @@
 
 // tcg includes
 #include "macros.h"
+#include <algorithm>
 
 /*!
   \file     tcg_poly_ops.h